Finds the last character equal to none of the characters in the given character sequence. The search considers only the interval [0; pos]. If the character is not present in the interval, npos will be returned.

1) Finds the last character equal to none of characters in str.

2) Finds the last character equal to none of characters in the first count characters of the character string pointed to by s. s can include null characters.

3) Finds the last character equal to none of characters in character string pointed to by s. The length of the string is determined by the first null character.